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The moose likes Developer Certification (SCJD/OCMJD) and the fly likes ICMP and RMI Big Moose Saloon
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Ronald Wouters
Ranch Hand

Joined: Apr 28, 2005
Posts: 190
Hi all,
during testing of RMI for URLyBird I discovered that apparently ICMP needs to be enabled on my firewall for RMI to work correctly.
Below you see the output of an "Ethereal" network scan.
You can clearly see that after data is returned from my server ( to my client (, there is an ICMP entry in the logfile of the scan saying "Destination unreachable (Host administratively prohibited)".
If I shutdown the firewall on my server, everything works just fine.
So, what gives ? Why is ICMP needed during an RMI "conversation" ?
No. Time Source Destination Protocol Info
12 2006-01-31 05:40:30.010969 RMI JRMI, ReturnData

Frame 12 (300 bytes on wire, 300 bytes captured)
Ethernet II, Src: Xinetron_12
Internet Protocol, Src: (, Dst: (
Transmission Control Protocol, Src Port: 1099 (1099), Dst Port: 32867 (32867), Seq: 19, Ack: 82, Len: 234
Java RMI
Java Serialization

No. Time Source Destination Protocol Info
15 2006-01-31 05:40:30.187560 ICMP Destination unreachable (Host administratively prohibited)

Frame 15 (102 bytes on wire, 102 bytes captured)
Ethernet II, Src: Xinetron_12
Internet Protocol, Src: (, Dst: (
Internet Control Message Protocol

[ January 30, 2006: Message edited by: Ronald Wouters ]

Sun Certified Developer for the Java 2 Platform
Sun Certified Enterprise Architect for the Java Platform, Enterprise Edition 5
I agree. Here's the link:
subject: ICMP and RMI
It's not a secret anymore!